Project Summary The proposed study will adapt and test a low resource school-based intervention to prepare students with ADHD for the transition to high school?a point of vulnerability for youth with ADHD (Kent et al., 2011). The resulting intervention will be delivered as a peer-delivered orientation to high school (1-2 weeks for 4 hours a day) with weekly peer-delivered support during the first 16 weeks of the ninth grade year. Intervention development will involve scaling down an intensive Summer Treatment Program for adolescents with ADHD (Sibley et al., 2018), using its core components (i.e., daily skills training and repetition, parent coaching in contingency management, engaging recreational activities) to bolster a promising peer-delivered school-based intervention for ninth graders with ADHD (i.e., STRIPES; Sibley et al., under review). The resulting intervention (summer STRIPES) will target three mechanisms that are critical markers of high school success: (a) intrinsic motivation, (b) extrinsic motivation, and (c) executive functions (EFs). Y01, will use a stakeholder informed process to iteratively adapt the intervention with input from two partnering high schools (i.e., administrators, counselors, teachers, parents, students) and content experts (Sibley, Langberg, Sasser, Aaronson). Two manuals that are individualized for each school will emerge. A total of 72 rising ninth grade students with ADHD will be recruited in Y02 and Y03 (36 per year; 18 per school) from two high schools randomly assigned (within school) to receive summer STRIPES or enhanced school services as usual (SSU plus). A project school mental health specialist will be engaged to train a school staff summer STRIPES sponsor at each school, who will oversee training and supervision peer interventionists with support from investigators. Peer interventionists will receive a three-day training and weekly supervision. Study assessments will occur at baseline and three follow-up points throughout the ninth grade year. To test the intervention?s preliminary effectiveness, the study will examine treatment effects on GPA, class attendance, and disciplinary incidents. Preliminary effectiveness will also be measured through indices of engagement (parent, adolescent, peer attendance, ratings of satisfaction, perceived utility, and therapeutic alliance) and school fit (treatment fidelity, peer attitudes toward treatment). To detect whether therapeutic mechanisms (intrinsic motivation, extrinsic motivation, EFs) are engaged by summer STRIPES, we will test for group differences on multi-method indices of these mechanisms, as well as the extent to which hypothesized mechanisms affect meaningful change on study outcomes. This project represents the first attempt to utilize a peer-delivered model for ADHD intervention in a high school orientation context. If summer STRIPES participants show meaningful improvements in functioning and engagement and school fit are strong, an R01 will be planned to fully evaluate the effectiveness of this approach. To inform this future trial, attention will be given to developing an optimal measurement battery, treatment delivery model, and recruitment strategy for rising ninth graders.